1. Field of the Invention
The invention relates to a printing apparatus and a feeding control method.
2. Description of the Related Art
In a printing apparatus for printing an image on a web (for example, a roll sheet), although the web is fed by two feeding units, i.e., a printing feeding unit and a fixing feeding unit, since the printing feeding unit and the fixing feeding unit have a different driving source respectively, a difference occurs in web feed amounts by the two driving sources. To cope with the problem, the printing apparatus interposes a buffer unit having a buffer plate which generates reaction force in a direction and makes a circular arc motion between the printing feeding unit and the fixing feeding unit; and the difference between the web feed amounts is absorbed by changing an angle of the buffer plate.
When the angle of the buffer plate exceeds a predetermined range, there is a possibility that the web is break off, whereas when the angle of the buffer plate becomes smaller than the predetermined range, there is a possibility that the web is defectively fed due to an insufficient amount of tension. Accordingly, in the printing apparatus, it is necessary to control a feed of the web so that the angle of buffer plate falls within a predetermined range.
However, it is necessary for the printing feeding unit to feed the web so that a toner image is transferred to a determined position of the web in a printing unit. Accordingly, in the printing apparatus, ordinarily, the fixing feeding unit feeds the web so that the angle of buffer plate falls within the predetermined range.
When the feed of the web is stopped, it is necessary for the fixing feeding unit to generate brake force so that the feed of the web is stopped in a state that the angle of the buffer plate falls within the predetermined range, therefore, an optimum value of the brake force to be generated is different depending on a friction load of the web to the fixing feeding unit and a load of the web (sheet).
For example, Japanese Patent Application Laid-open No. 2011-170324 discloses a technology for determining brake force that is used to stop a feed of a web next time from a buffer amount of a buffer plate when the feed of the web is stopped.
For example, Japanese Patent Application Laid-open No. 2007-316411 discloses a technology for adjusting brake force based on a change of a feed amount of a web per each minute unit time when a feed of the web is decelerated.
Further, for example, Japanese Patent Application Laid-open No. 61-098373 discloses a technology for detecting a cycle of generation of encoder pulses generated by a rotation of a driving source; determining brake force according to the detected cycle of generation of the encoder pulses; generating the determined brake force; and decelerating and stopping a feed of a web.
However, in the technology disclosed in Japanese Patent Application Laid-open No. 2011-170324, since it is at the time when the feed of the web is stopped next time that optimum brake force is reflected, there is a possibility that the buffer plate cannot be stopped in an appropriate range at the time when for example the web is replaced and the like.
In the technology disclosed in Japanese Patent Application Laid-open No. 2007-316411, since there is a case in which it is difficult to identify the change of the feed amount per each minute unit time in a case in which the web is likely to stop and in a case the web is not likely to stop, there is a possibility that the buffer plate cannot be stopped in an appropriate range.
Further, in the technology disclosed in Japanese Patent Application Laid-open No. 61-098373, when, for example, a difference exists between loads of webs, there is a possibility that the buffer plate cannot be stopped in an appropriate range.
There is a need to provide a printing apparatus and a feeding control method capable of causing an angle of a buffer plate to be fallen within an appropriate range without depending on a type of a web.